The induction of antigen-specific T cell responses involves multiple interactions between cell surface receptors on T cells and ligands on antigen presenting cells (APCs). The primary interaction is between the T cell receptor (TCR)/CD3 complex on a T cell and a major histocompatibility complex (MHC) molecule/antigenic peptide complex on an antigen presenting cell. This interaction triggers a primary, antigen-specific, activation signal in the T cell. In addition to the primary activation signal, induction of T cell responses requires a second, costimulatory signal. In the absence of proper costimulation, TCR signalling can induce a state of anergy in the T cell. Subsequent appropriate presentation of antigen to an anergic T cell fails to elicit a proper response (see Schwartz, R. H. (1990) Science 248:1349).
A costimulatory signal can be triggered in a T cell through a T cell surface receptor, such as CD28. For example, it has been demonstrated that suboptimal polyclonal stimulation of T cells (e.g. by anti-CD3 antibodies or phorbol ester, either of which can provide a primary activation signal) can be potentiated by crosslinking of CD28 with anti-CD28 antibodies (Linsley, P. S. et al. (1991) J. Exp. Med. 173:721; Gimmi, C. D. et al. (1991) Proc. Natl. Acad. Sci. USA 88:6575). Moreover, stimulation of CD28 can prevent the induction of anergy in T cell clones (Harding, F. A. (1992) Nature 356:607-609). Natural ligands for CD28 have been identified on APCs. CD28 ligands include members of the B7 family of proteins, such as B7-1(CD80) and B7-2 (B70) (Freedman, A. S. et al. (1987) J. Immunol. 137:3260-3267; Freeman, G. J. et al. (1989) J. Immunol. 143:2714-2722; Freeman, G. J. et al. (1991) J. Exp. Med. 174:625-631; Freeman, G. J. et al. (1993) Science 262:909-911; Azuma, M. et al. (1993) Nature 366:76-79; Freeman, G. J. et al. (1993) J. Exp. Med. 178:2185-2192). In addition to CD28, proteins of the B7 family have been shown to bind another surface receptor on T cells related to CD28, termed CTLA4, which may also play a role in T cell costimulation (Linsley, P. S. (1991) J. Exp. Med. 174:561-569; Freeman, G. J. et al. (1993) Science 262:909-911).
The elucidation of the receptor:ligand relationship of CD28/CTLA4 and the B7 family of proteins, and the role of this interaction in costimulation, has led to therapeutic approaches involving manipulation of the extracellular interactions of surface receptors on T cells which bind costimulatory molecules. For example, a CTLA4Ig fusion protein, which binds to both B7-1 and B7-2 and blocks their interaction with CD28/CTLA4, has been used to inhibit ejection of allogeneic and xenogeneic grafts (see e.g., Turka, L. A. et al. (1992) Proc. Natl. cad. Sci. USA 89:11102-11105; Lenschow, D. J. et al. (1992) Science 257:789-792). Similarly, antibodies reactive with B7-1 and/or B7-2 have been used to inhibit T cell proliferation and IL-2 production in vitro and inhibit primary immune responses to antigen in vivo (Hathcock K. S. et al. (1993) Science 262:905-907; Azuma, M. et al. (1993) Nature 366:76-79; Powers, G. D. et al. (1994) Cell. Immunol. 153:298-311; Chen C. et al. (1994) J. Immunol. 152:2105-2114). Together, these studies indicate the costimulatory pathway mediated by T cell surface receptors which bind costimulatory molecules such as B7-1 and B7-2 are desirable targets for manipulating immune responses. Delivery of an antigen specific signal to a T cell in the absence of a costimulatory signal does not induce a T cell response, but rather has been found to induce a state of T cell unresponsiveness or anergy (see Schwartz, R. H. (1990) Science 248:1349; Jenkins, M. K. et al. (1988) J. Immunol. 140:3324). In a number of clinical situations it is desirable to inhibit T cell responses (e.g., in transplantation or autoimmune disorders). Thus, therapeutic approaches have been proposed to induce antigen specific T cell unresponsiveness by blocking of a costimulatory signal in T cells. For example, a CTLA4Ig fusion protein, which binds both B7-1 and B7-2, has been used to inhibit rejection of allogeneic and xenogeneic grafts (see e.g., Turka, L. A. et al. (1992) Proc. Natl. Acad. Sci. USA 89, 11102-11105; Lenschow, D. J. et al. (1992) Science 257, 789-792). Similarly, antibodies reactive with B7-1 and/or B7-2 have been used to inhibit T cell proliferation and IL-2 production in vitro and inhibit primary immune responses to antigen in vivo (Hathcock K. S. et al. (1993) Science 262, 905-907; Azuma, M. et al. (1993) Nature 36:76-79; Powers, G. D. et al. (1994) Cell. Immunol. 153, 298-311; Chen C. et al. (1994) J. Immunol. 152, 2105-2114).
When stimulated through the T cell receptor(TCR)/CD3 complex without requisite costimulation through the CD28/B7 interaction, T cells enter a state of antigen specific unresponsiveness or anergy. This invention is based, at least in part, on the discovery that signaling though a common cytokine receptor xcex3 chain (e.g., interleukin-2 receptor, interleukin-4 receptor, interleukin-7 receptor) prevents the induction of T cell anergy. This xcex3 chain has been found to be associated with a JAK kinase having a molecular weight of about 116 kD (as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis) and signaling through the xcex3 chain induces phosphorylation of the JAK kinase.
Accordingly, one embodiment of this invention pertains to methods for stimulating proliferation by a T cell which expresses a cytokine receptor xcex3 chain and which has received a primary activation signal under conditions which normally result in unresponsiveness in the T cell (i.e., lack of costimulation). T cell unresponsiveness or anergy is prevented by contacting T cells with an agent which binds to the cytokine receptor xcex3 chain and stimulates an intracellular signal in the T cell resulting in T cell proliferation. Typically, the agent is an anti-xcex3 chain antibody capable of crosslinking the receptor or a soluble form of natural ligand which binds to the xcex3 chain, such as interleukin-4 or interleukin-7. Alternatively, T cells can be contacted with an agent which acts intracellularly to stimulate phosphorylation of the 116 kD JAK kinase. To induce an immune response against a pathogen, such as a virus, bacteria or parasite in vivo the pathogen or component thereof can be administered in conjunction with an agent which binds to the cytokine receptor xcex3 chain and stimulates an intracellular signal in the T cell. Similarly, tumor immunity can be can be induced in a tumor bearing host in vivo or ex vivo by contacting T cells of the subject in the presence of tumor cells expressing tumor antigens with a xcex3 chain stimulatory agent (e.g., a crosslinking anti-xcex3 chain antibody).
Another embodiment of the invention pertains to methods for inducing unresponsiveness to an antigen in a T cell which expresses a cytokine receptor xcex3 chain. T cells are contacted in vivo or ex vivo in the presence of an antigen with an agent which inhibits delivery of a signal through the cytokine receptor xcex3 chain resulting in T cell unresponsiveness to the antigen. Such agents can act extracellularly to inhibit delivery of a signal through the xcex3 chain, such as an inhibitory or blocking anti-xcex3 chain antibody or an agent which binds a natural ligand of the xcex3 chain to inhibit binding of the ligand to the 7 chain (e.g., an anti-interleukin-2 antibody, an anti-interleukin-4 antibody or an anti-interleukin-7 antibody). Alternatively, the agent can act intracellularly to inhibit delivery of a signal through the cytokine receptor xcex3 chain, such as an agent which inhibits association of the xcex3 chain with the 116 kD JAK kinase or inhibits phosphorylation of the xcex3 chain or the JAK kinase or both. Methods for inducing T cell unresponsiveness are particularly useful for inhibiting transplant rejection and graft-versus-host disease and for treating autoimmune diseases.
Method for identifying agents which stimulate or inhibit delivery of a signal through a cytokine receptor xcex3 chain on a T cell are also within the scope of this invention. These and other embodiments of the invention are described in further detail herein.